In recent years, since ink-jet recording enables simple and less expensive formation of images, it has been applied to various printing fields such as photography, various types of printing, marking, and special printing such as color filters. Specifically, by employing ink-jet recording apparatuses which eject and control minute ink droplets, ink-jet inks whose range of color reproduction, durability, and ejection adaptability have been enhanced, and paper or media for ink-jet printing use whose ink-absorbability, color forming properties of colorants and surface glossiness have also been markedly enhanced, it has become possible to provide image quality comparable to conventional silver halide photography.
However, the ink-jet image recording system which requires special paper or media for ink-jet printing use causes problems such as restriction of recording media usable in the system, and a subsequent cost increase in the recording media.
On the other hand, in the offices, needs for a system which enables high-speed full-color printing employing plain paper has been increasing. Further, with regard to composition of ink-jet ink, various studies have been undertaken with regard to factors such as high-speed printintability, excellent reproducibility of text on plain paper, minimal rear surface penetration (a phenomenon in which the printed ink penetrates through the recording medium to result in appearance of the printed image on the reverse surface of the recording medium), inhibition of curling, more rapid penetration of ink into the paper and quick dryability (as described in, for example, Patent Documents 1 and 2).
With regard to the above problems, the inventors found an ink which enables to simultaneously prevent both the curling and the rear surface penetration by employing an ink-jet ink composed of, as solvents, a small amount of water and a large amount of a specific high boiling organic solvent, whereas solvents used for a conventional water-based ink-jet ink are composed of a small amount of high boiling organic solvent and a large amount of water (as described in, for example, Patent Documents 3-6). In particular, a monool having one hydroxyl group is preferable as the high-boiling organic solvent.
However, it was found that when prints printed with an ink of the invention are kept in piles with electrophotographic prints, mutual adhesion of electrophotographic prints may occur. For the reason of the adhesion, it was found that since the ink of this invention incorporates much more high boiling organic solvent than common water-based inks, the ink tend to remain in paper, dissolving electrophotographic toners.                Patent Document 1: Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 2004-217930        Patent Document 2: JP-A 2005-193660        Patent Document 3: JP-A 2005-220218        Patent Document 4: JP-A 2005-220296        Patent Document 5: JP-A 2005-220297        Patent Document 6: JP-A 2005-220298        Patent Document 7: JP-A 2001-322275        